Skip to content
UCH

How big is it really? A visual unit comparison

Length, area, volume, mass, or speed — compare two real-world objects and see the ratio on a log-scale chart. Useful for writing, homework, and settling arguments.

First thing
0.15 m
vs second thing
0.30 m
The answer
iPhone (long side) is 2.02× smaller than A4 page (long side).

You'd need 2 of a iPhone (long side) to match one A4 page (long side).

All length references (log scale)

Why numbers alone fail

Tell someone a building is 381 m tall and they nod. Tell them "as tall as the Empire State Building" and they picture it. The brain is reference-hungry: a bare number is a symbol, a known object is a body- level intuition. This tool is a ratio machine — you pick two things you sort-of know, and it tells you how much bigger, smaller, or faster one is than the other. Good for writing, teaching, planning, and arguing.

A few of our favorite surprises: a typical backyard pool holds about as much water as 10,000 milk jugs. Usain Bolt's top sprint speed (10.4 m/s) would be just barely competitive against a fast urban driver at 14 m/s (31 mph) — for a few seconds, before the car wins. An African elephant weighs as much as 66 house cats or a bit over four compact cars. A standard football field is 5× the area of a tennis court but only 1/640 of Central Park.

Length: a grounding map from phones to marathons

Length is the easiest dimension to build intuition for because it's one-dimensional and you can often pace it out. A standard US parking space is 9 × 18 ft — a human body is roughly two parking space widths and one length tall. A football field is the length of a Boeing 747-8 plus another third. A marathon is the length of Manhattan (north-south) multiplied by two. Central Park is roughly 4 km long, about a twelfth of a full marathon.

The one-order-of-magnitude rule is a useful sanity check. If the chart shows one thing as 10× another, that's a real leap — double the body length in every direction, ten times the area per face, a thousand times the volume. When someone claims their new house is "twice as big" at 1,800 ft² vs 900 ft², the dimension ratio (same house shape but stretched) is only 1.4×.

Area: where the ratios balloon

Area is where most human intuition breaks. A 10×10 ft room feels small (100 ft²). A 20×20 ft room feels "about double" but is actually four times the area (400 ft²). A backyard that is 40×40 ft is 16× the room, not 4×. The fact that area scales as the square of length is why a "double-sized" pizza usually costs less than twice as much — you're getting 4× the pizza for maybe 1.7× the price.

For city-scale comparison, 1 acre is about 3/4 of a football field, or roughly the size of a small neighborhood block. Central Park is 843 acres. Monaco, an actual country, is 499 acres — smaller than Central Park by a factor of 1.7.

Volume: the dimension that hides in plain sight

A standard bathtub holds about 150 L of water, which is about 40 US gallons. A car gas tank averages 57 L (15 gal), nearly half a tub. A typical backyard pool is 38,000 L — 250 bathtubs. An Olympic pool is 2.5 million L — 16,600 bathtubs. When you stack these up visually on a log scale, you see why water conservation guidance focuses on the big ratios (pool covers, landscaping) and not the small ones (toothbrush timing) — the orders of magnitude are wildly different.

Mass: humans are denser than you think

An average American adult male is 90.6 kg, almost exactly the mass of a medium-size refrigerator (90 kg). A house cat at 4.5 kg is 20 adult iPhones. A grand piano at 450 kg is 5 adults. A London bus at 12,000 kg is 130 adults or 2 African elephants. These bodily anchors are worth internalizing because news stories almost never report mass with reference — "a 300-kg object fell" is harder to feel than "a grand piano's worth."

Speed: why highway driving is the world's forgotten fast

A casual walk is 1.4 m/s. A casual cyclist is 5.5 m/s — four times a walker. Usain Bolt at his peak hit 10.4 m/s, which is seven times a walker and roughly the top speed of a cheetah (31 m/s is the pop number; peer-reviewed observations are lower). Highway driving at 30 m/s (67 mph) is three times a sprinting cheetah and thirty times a walker. A commercial jet at cruise is nearly the speed of sound at sea level. This is why even at highway speeds, the aerodynamic drag on a car doubles roughly every 30 km/h — drag scales with the square of velocity, and at 100 km/h you're already fighting a non-trivial wall.

Useful related tools

Frequently Asked Questions

Because the real world spans orders of magnitude. A house cat and an African elephant are both in the 'mass' category but differ by a factor of 1,300. On a linear scale the cat would be invisible. A log scale shows ratios clearly — every step on the axis is a multiply, not an add. That's how we intuitively think about 'how much bigger' anyway: 2× is different from 1.5×, regardless of what the absolute numbers are.